Alcohol-positive trauma patients are more likely to be readmitted to a trauma center or die from a subsequent injury than are alcohol-negative trauma patients. Despite their increased risk, there are few empirically-supported treatments available for this population. Admission to a trauma unit may represent a "teachable moment", where patients are particularly willing to discuss their alcohol use. Therefore, interventions delivered in the trauma unit may be particularly effective. Motivational Interviewing (MI), a brief, directive, non-confrontational intervention, has demonstrated some promise in this setting. Further, inclusion of a significant other (SO) in prolonged, intensive alcohol treatment appears to improve treatment retention and efficacy. Although inclusion of an SO in MI has been suggested, there are few data to support this endorsement. Accordingly, this study (N=300) will address whether motivational interviewing including both the trauma patient and an SO can more effectively decrease and maintain reductions in alcohol use and alcohol-related problems 6 and 12 months following discharge from the trauma unit than MI with the individual patient or an assessment-only condition. The 2 MI groups will each receive 2 intervention sessions timed to occur in the hospital, and 1 booster session, occurring 1 month following discharge. In the assessment-only condition, patients will receive only assessment of their drinking at baseline. This proposal will allow us to address the next phase of our program of research designed to develop easily disseminable treatments for these high-risk populations in medical settings. This study will also address potential mediators (motivation to change alcohol use, self-efficacy, alcohol treatment attendance, and social support for abstinence) and moderators of MI effects. The cost-effectiveness of the intervention will also be addressed. Thus, this study will address both a significant public health problem and provide important information about MI mechanisms that may be relevant to the broader addiction treatment community.